Showing papers on "Thermogravimetric analysis published in 2007"

Manganese oxide catalysts for NOx reduction with NH3 at low temperatures

Abstract: Manganese oxide catalysts prepared by a precipitation method with various precipitants were investigated for the low temperature selective catalytic reduction (SCR) of NOx with NH 3 in the presence of excess O 2 . Various characterization methods such as N 2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA) and X-ray absorption near edge structure (XANES) were conducted to probe the physical and chemical properties of MnOx catalysts. The active MnOx catalysts, precipitated with sodium carbonate and calcined in air at moderate temperatures such as 523 K and 623 K, have the high surface area, the abundant Mn 4+ species, and the high concentration of surface oxygen on the surface. The amorphous Mn 3 O 4 and Mn 2 O 3 were mainly present in this active catalyst. The carbonate species appeared to help adsorb NH 3 on the catalyst surface, which resulted in the high catalytic activity at low temperatures.

Phosphonic Acid-Modified Barium Titanate Polymer Nanocomposites with High Permittivity and Dielectric Strength

Abstract: Materials with high dielectric permittivity are important in electronic components such as capacitors, gate dielectrics, memories, and power-storage devices. Conventional highpermittivity materials such as barium titanate (BT) can be processed into thin films by using chemical solution deposition yielding a relative permittivity (er) of about 2500 and relatively low dielectric loss but require high-temperature sintering, which is not compatible with many substrate materials. Polymer-based dielectrics, such as biaxially oriented polypropylene (BOPP), have good processability with high dielectric strengths (∼ 640 V lm) suitable for high-energy-density capacitors, but the storage capacity (ca. 1–1.2 J cm) is limited by the low er (ca. 2.2) of these materials. [6] Various approaches to high-er materials based on nanocomposites containing metal particles or other conductive materials have been pursued. Such nanocomposites have afforded huge er values but the resulting materials are limited by the high-temperature processing required, high dielectric loss, or low dielectric strength. Polymer/ceramic nanocomposites in which high-er metal oxide nanoparticles such as BT and lead magnesium niobate–lead titanate (PMN–PT) are incorporated into a polymer host are of significant current interest. The combination of high-er nanoparticles with high-dielectric-strength polymer hosts offers the potential to obtain processable highperformance dielectric materials. Simple solution processing of BT particles in a polymer host generally results in poor film quality and inhomogeneities, which are mainly caused by agglomeration of the nanoparticles. Addition of surfactants, such as phosphate esters and oligomers thereof, can improve the dispersion of BT nanoparticles in host polymers and consequently the overall nanocomposite film quality. However, in such systems, residual free surfactant can lead to high leakage current and dielectric loss. Thus, approaches to bind surface modifiers to BT nanoparticles via robust chemical bonds are highly desirable. Ramesh et al. have reported on the use of trialkoxysilane surface modifiers for the dispersion of BT nanoparticles in epoxy polymer hosts resulting in nanocomposites with reasonably high er, up to 45. [12] With the objective of identifying ligands that can form stable bonds to a BT surface through coordination or condensation, we have investigated a series of different ligand functionalities. In this Communication, we report that phosphonic acid ligands effect robust surface modification of BT and related nanoparticles and that the use of particles modified with suitable phosphonic acid ligands leads to well-dispersed BT nanocomposite films with high er and high dielectric strength. We have investigated the binding of a variety of ligands to the surface of BT nanoparticles, as the stability of the binding on the surface is vital to effective surface modification. We examined the following set of ligands, each bearing an aliphatic octyl chain with a different terminal binding group: C8H17-X, where X = PO(OH)2 (OPA), SO2ONa (OSA), Si(OCH3)3 (OTMOS), and CO2H (OCA). Trialkoxysilanes are widely used surface modifiers for silicate, indium tin oxide, and other metal oxide surfaces. Phosphonic acids have been reported to modify TiO2, ZrO2, and indium tin oxide surfaces and are thought to couple to the surface of metal oxides either by heterocondensation with surface hydroxyl groups or coordination to metal ions on the surface. Carboxylic acid and sulfonic acid groups may also bind to the surface in a similar manner. A sample of each ligand was mixed with BT nanoparticles (30–50 nm, 0.5 mmol ligand/ g BT) in an ethanol/water solution and stirred at 80 °C, followed by extensive washing with ethanol or water and centrifugation to remove excess and/or physisorbed ligand. The treated BT nanoparticles were dried and characterized by using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). Figure 1a shows a comparison of FTIR spectra in the C–H stretching region for the BT nanoparticles treated with the ligands described above, followed by washing. These results C O M M U N IC A IO N

Monitoring oxidation of multiwalled carbon nanotubes by Raman spectroscopy

Abstract: Multiwalled carbon nanotubes (MWCNTs) were oxidized in air and acids while varying the treatment time and/or temperature. The goal of this approach was to create the highest density of carboxyl groups with moderate sample loss, which is necessary for nanocomposite applications. In situ Raman experiments allowed real-time observation of the structural changes in MWCNTs upon oxidation. The ratio of the Raman intensities of the D and G bands was used to estimate the concentration of defects. It was found that while an oxidation for 6 h in H2SO4/HNO3 provided the strongest effect, a ‘flash oxidation’ in air (15 min at 550 °C) also leads to an efficient functionalization in a cost-effective and environmentally friendly way. Transmission electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis and electrophoretic mobility analysis were used to study the oxidized nanotubes. Copyright © 2007 John Wiley & Sons, Ltd.

Characterization of bio-oils in chemical families

Abstract: This paper describes an analytical approach to determine the chemical composition of bio-oils in terms of macro-chemical families. Bio-oils from the vacuum pyrolysis of softwood bark and hardwood were first fractionated using solvent extraction. Fractions obtained were then characterized using GC-MS, thermogravimetric techniques (TG) and Gel Permeation Chromatography (GPC). Thermogravimetric and molar mass distribution curves of each fraction were interpreted in terms of macro-families applying curve-fitting procedures. The composition of the different macro-fractions obtained was in agreement using both methods. The proposed procedure enables a thorough description of bio-oil composition as a mixture of water, monolignols, polar compounds with moderate volatility, sugars, extractive-derived compounds, heavy polar and non-polar compounds, MeOH–toluene insolubles and volatile organic compounds.

Evolution of structure during the oxidation of zirconium diboride–silicon carbide in air up to 1500 °C

Abstract: The structures that developed as dense ZrB2–SiC ceramics were heated to 1500 °C in air were characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction. The oxidation behavior was also studied using thermal gravimetric analysis (TGA). Below 1200 °C, a protective B2O3-rich scale was observed on the surface. At 1200 °C and above, the B2O3 evaporated and the SiO2-rich scale that formed was stable up to at least 1500 °C. Beneath the surface, layers that were rich in zirconium oxide, and from which the silicon carbide had been partially depleted, were observed. The observations were consistent with the oxidation sequence recorded by thermal gravimetric analysis.

Influence of limestone powder used as filler in SCC on hydration and microstructure of cement pastes

Abstract: In recent years, self-compacting concrete (SCC) has gained wide application in the construction industry. As for high performance concrete (HPC) and traditional concrete (TC), the microstructural properties of SCC are the main factors, which determine the material properties, i.e. the mechanical properties, transport properties and the durability behaviour. In order to investigate the development of the microstructure of SCC, the microstructural parameters of the paste including porosity, pore size distribution and phase distribution are determined by means of mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). The thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) are used to identify the phase constituents. These parameters as studied for self-compacting concrete are compared with high performance concrete and traditional concrete. The specimens of self-compacting cement paste (SCCP) are made with water/binder ratio 0.41 and 0.48, the high performance cement paste (HPCP) with w/c 0.33 and traditional cement paste (TCP) with w/c 0.48. The measurements are performed at different hydration stages, i.e. at 1, 3, 7, 14, 28 and 56 days. The result of this research shows that the pore structure, including the total pore volume, pore size distribution and critical pore diameter, in the SCCP is very similar to that of HPCP. The fact that limestone powder does not participate in the chemical reaction was confirmed both from thermal analysis and BSE image analysis.

Synthesis and properties of magnesium tetrahydroborate, Mg(BH4)2

Abstract: Mg(BH4)2 is one of the few complex hydrides which have the potential to meet the requirements for hydrogen storage materials, because it contains 14.9 mass% H and has suitable thermodynamic properties. It has not been investigated for hydrogen storage applications yet. In this study, several ways to synthesize solvated and desolvated magnesium tetrahydroborate by wet chemical and mechanochemical methods were tested and compared. A direct synthesis by a reaction of MgH2 with aminoboranes yields magnesium tetrahydroborate quantitatively and in pure form. The method is also applicable to the synthesis of other tetrahydroborates. The products were characterized by elemental analysis, in situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermal analysis methods, such as thermogravimetric analysis (TGA-DSC) and high-pressure calorimetry under a hydrogen atmosphere (HP-DSC).

Morphology, dynamic mechanical and thermal studies on poly(styrene-co-acrylonitrile) modified epoxy resin/glass fibre composites

Abstract: Poly(styrene-co-acrylonitrile) (SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRPs) in order to get improved mechanical and thermal properties. E-glass fibre was used as the fibre reinforcement. The morphology, dynamic mechanical and thermal characteristics of the systems were analyzed. Morphological analysis revealed heterogeneous dispersed morphology. There was good adhesion between the matrix polymer and the glass fibre. The dynamic moduli, mechanical loss and damping behaviour as a function of temperature of the systems were studied using dynamic mechanical analysis (DMA). DMA studies showed that DDS cured epoxy resin/SAN/glass fibre composite systems have two Tgs corresponding to epoxy rich and SAN rich phases. The effect of thermoplastic modification and fibre loading on the dynamic mechanical properties of the composites were also analyzed. Thermogravimetric analysis (TGA) revealed the superior thermal stability of composite system.

Experimental study on the thermal and mechanical properties of multi-walled carbon nanotube-reinforced epoxy

Abstract: In this study, multi-walled carbon nanotubes (CNTs) were infused into Epon 862 epoxy through a high intensity ultrasonic liquid processor and then mixed with EpiCure curing agent W using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and flexural tests were performed on unfilled, 0.1, 0.2, 0.3, and 0.4 wt% CNT-filled epoxy to identify the loading effect on the thermal and mechanical properties of composites. DMA studies revealed that filling the carbon nanotube into epoxy can produce a 90% enhancement in storage modulus and a 22 °C increase in Tg. However, due to the lower crosslink density of the nanophased systems, a 6 °C decrease in decomposition temperature was observed in the 0.4 wt% CNT/epoxy in the TGA test. The flexural results showed that modulus increased with higher CNT loading percentages and the 0.3 wt% CNT-infusion system showed the maximum strength enhancement. Based on the experiment's results, a nonlinear constitutive equation was established for neat and nanophased epoxy.

Self-assembly directed synthesis of poly(ortho-toluidine)-metal(gold and palladium) composite nanospheres.

Abstract: Poly(ortho-toluidine) (POT)-gold (Au) and palladium (Pd) composite nanospheres were successfully synthesized by the reaction of o-toluidine with the corresponding metal (Au or Pd) colloidal solution through self-assembly process in the presence of dodecylbenzenesulfonic acid (DBSA), which acts as both a dopant and surfactant, and ammonium peroxydisulfate as an oxidizing agent. The composites (POT-DBSA/Au or Pd) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, UV-Visible (UV-Vis) spectroscopy, and electrical conductivity measurements. TEM images of the nanocomposites reveal that metal (Au or Pd) nanoparticles were well dispersed on POT spheres. TGA and XRD results show that the composites exhibit high thermal stability and are more crystalline compared with pristine POT. It was found that the electrical conductivity of the POT-DBSA/Au or Pd composites is 2 orders of magnitude higher than that of pristine polymer. Also, the POT-DBSA/Pd composite exhibits magnetic property. The formation mechanism of the POT-DBSA/Au or Pd composite nanosphere is discussed.

Composites of poly(L‐lactide) with hemp fibers: Morphology and thermal and mechanical properties

Abstract: Composites of poly(L-lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight-average molecular weight = 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA–PEG/hemp composites were analyzed as a function of the fiber amount. The cold-crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70–130°C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 110°C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber-filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 255–268, 2007

Kinetic and Reaction Mechanism of CO2 Sorption on Li4SiO4: Study of the Particle Size Effect

Abstract: Lithium orthosilicate (Li4SiO4) was synthesized by three different techniques: the solid-state reaction, precipitation, and sol−gel (using a microwave oven) methods. The better results were obtained by the two first methods. In the third case, pure Li4SiO4 could not be obtained, because the microwaves produced the lithium sublimation. The samples were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption, and thermogravimetric analysis under a flux of CO2. Different particles sizes were obtained as a function of the method of synthesis, and the CO2 sorption analyses gave different results. The particle size modified the stability of the Li4SiO4 during the CO2 sorption/desorption cycles, due to lithium sublimation, as Li2O. Conversely, the isothermal study allowed measuring the kinetic parameters for the chemisorption and diffusion processes, as a function of the particle size. As could be expected, the activation energies obtained, for the small particles, were smaller than thos...

Synthesis of Sulfonated Polybenzimidazoles from Functionalized Monomers: Preparation of Ionic Conducting Membranes

Abstract: In the present work, a new sulfonated tetraamine and the corresponding sulfonated polybenzimidazoles (sPBI) were synthesized. For the sake of determining the best polymerization conditions, a study involving model compounds was first performed. A strong acid medium was used as polymerization solvent, which allowed to obtain high molecular weight sPBI. A series of polymers with ion exchange capacity (IEC) ranging from 0 to 2.6 mequiv/g were synthesized using a non-sulfonated tetraamine as a comonomer. The chemical structure of those polymers was confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) as well as by titration. Thermogravimetric analysis (TGA) and viscosity measurement were performed as well. On the other hand, different architectures of the copolymers were prepared, i.e., random, sequenced copolymers, and blends of the homopolymers. The membranes prepared from the sPBI display low water uptake. The ionic conductivities measured in the hydrated state at room temper...

Thermally conductive silicone rubber reinforced with boron nitride particle

Abstract: Thermally conductive silicone rubber used as elastomeric thermal pad is successfully developed with boron nitride powder as conductive filler. The effects of content and particle size of filler on the thermal conductivity and mechanical property of silicone rubber are investigated. The results indicate that the use of hybrid boron nitride with three different particle sizes at a preferable weight ratio gives silicone rubber better thermal conductivity compared with each boron nitride with single particle size at the same total filler content. Furthermore, scanning electron microscopy, differential scanning calorimeter, thermogravimetric, etc., are used to characterize the morphology, curing behavior, thermal stability, and coefficient of thermal expansion (CTE) of the silicone rubber composites. POLYM. COMPOS., 28:23–28, 2007. © 2007 Society of Plastics Engineers